1. Field of the Invention
This invention relates to one-way drive mechanisms and more particularly to an improved one-way pawl and ratchet type clutch mechanism of simplified construction and high torque transmitting capability.
2. Description of the Prior Art
One-way drive mechanisms, hereinafter generally referred to as clutches, are well known and used in a wide variety of applications ranging from low speed high torque ratchet mechanisms such as those employed in hand tools or wrenches to high speed transmission devices employed in complex drive systems for automobiles, aircraft, or the like where operating speeds ranging up to 20,000 rpm or higher may be encountered.
The known one-way clutches, particularly those employed for relatively high torque transmission, generally have taken the form of a pawl and ratchet drive mechanism, a roller and ramp or ball and ramp drive mechanism, or an overrunning sprag-type drive mechanism. Examples of known clutches employing pawl and ratchet drives may be found, for example, in U.S. Pat. Nos. 5,070,978 and 5,449,057, both of which disclose disc, or face plate type pawl and ratchet clutches, and in U.S. Pat. Nos. 4,437,553 and 4,788,847 in which the pawls move in a radial direction for engagement and/or disengagement. U.S. Pat. Nos. 2,240,359 and 3,997,041 disclose known overrunning sprag clutches, and the above-mentioned U.S. Pat. No. 5,070,978 also illustrates a typical prior art roller or ball-type clutch as well as known sprag clutches and radial movement pawl and ratchet clutches.
The close tolerance required for the production of the component parts, and the number and size of these component parts, of known one-way clutches employed for high speed, high torque application generally has made these devices relatively expensive to manufacture. Also, the number and size of the component parts has made the automated assembly of the completed devices difficult, or impossible, again adding to the cost of their production. Further, the complex structure of these devices has reduced their reliability and expected service life and can result excessive maintenance cost. While the initial cost of known one-way clutches might be relatively small compared to the overall cost of a complex machine such as an automatic transmission for a vehicle, the time and expense required to remove the transmission for repair has placed a premium on their reliability which can far exceed the initial cost of the clutch per se.
The known high speed pawl and ratchet clutches have generally employed a plurality of individual pawls or struts each located in a separate pocket or recess in either the driving or driven member, and a separate resilient means, typically a spring, also located in the respective pockets continuously urges the pawl into rubbing engagement with the other of the driving or driven member. These devices typically run in a lubricating fluid which tends to dampen movement of the pawls to provide smoother operation, but loss of lubrication or prolonged running with inadequate lubrication can produce erratic operation and damage to the clutch.
The clutch disclosed in the above-mentioned U.S. Pat. No. 5,070,978 attempts to overcome the problems encountered by the free floating pawls by mounting the pawls on a free floating or journaled carrier disc for movement between a driving position engaging recesses in both the driving and driven clutch plates and an overrunning position. Again, a plurality of pawls are required with pivot means mounting the respective pawls for limited movement relative to the carrier disc, and a separate spring member is required for each pawl.
A one-way clutch device suitable for use in low speed, low torque applications such as the automatic winding mechanism of a wrist watch is illustrated in U.S. Pat. No. 3,623,582. This clutch employs a drive disc mounted for free rotation on an arbor in opposed spaced relation to a driven disc fixedly mounted on the arbor. A wedging member journaled for free rotation on the arbor between the driving and driven plates has a plurality of radially extending arms each carrying an elongated arcuate wedging blade integrally formed on its end. The wedging blades have their opposed ends deflected in opposite directions axially of the arbor so as to rub one against each of the opposing faces of the driving and driven members and to be deflected thereby sufficiently to apply a twist or torque to the supporting radial arm. Each of the relatively rotating faces is provided with a plurality of circumferentially spaced driving recesses or openings into which the free ends of the projecting blades can deflect so that when the driving disc is rotated in one direction, the ends of the wedging blades will be deflected into the openings in the associated discs to interlock the two discs for simultaneous rotation. Conversely, upon relative rotation in the opposite direction, the wedging blades and supporting structure will float free, with the free ends of the wedging blades sliding over the driving openings. This arrangement inherently results in the possibility of substantial "dead motion", or relative rotation between the driving and driven members before the driving disc is locked to and commences to drive the driven disc. Since both ends of the wedging blades have to engage in an opening, the number of engagements is, in effect, doubled thereby inhibiting smooth operation of the device. Further, the offset or bent configuration of the wedging blades inherently results in substantial bending stress applied thereto, and the substantial length and curvature of the wedging blades greatly reduces their column strength so that the device is not well suited either for high speed operation or for the transfer of heavy torque loads.
It is accordingly a principal object of the present invention to provide an improved one-way clutch mechanism which has a minimum number of component parts and which overcomes the drawbacks of the known one-way clutches.
Another primary object of the present invention is to provide an improved one-way clutch suitable for the smooth reliable transfer of high torque loads and high speed operation.
It is another object of the invention to provide such a one-way clutch which is economical to manufacture and which is substantially maintenance free in operation.
It is another object of the present invention to provide such a one-way clutch in which the driving pawls or struts are rotatably fixed relation to and continuously urged into engagement with recesses in one of the driving or driven members whereby the free floating action is avoided.